Miniature implantable device and methods

ABSTRACT

Some implementations may provide an implantable wirelessly powered device that includes: one or more electrodes configured to apply one or more electrical pulses to an excitable tissue; and a first antenna configured to: receive, from a second antenna and through electrical radiative coupling, an input signal containing electrical energy, the second antenna being physically separate from the implantable device; and one or more circuits electrically connected to the first antenna, the circuits configured to: create the one or more electrical pulses suitable for stimulation of excitable tissue using the electrical energy contained in the input signal; and supply the one or more electrical pulses to the one or more electrodes, wherein the implantable device is shaped and arranged for delivery into a subject&#39;s body through an introducer or a needle of 18 gauge or smaller.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional Patent Application61/786,098, filed Mar. 14, 2013. Under 35 U.S.C. 365 and 120, thisapplication claims the benefit of and is a continuation in part of PCTapplication PCT/US2013/073326, filed Dec. 5, 2013, U.S. patentapplication Ser. No. 13/551,050 filed Jul. 17, 2012, U.S. patentapplication Ser. No. 14/045,764 filed Oct. 3, 2013, U.S. patentapplication Ser. No. 13/562,221, filed Jul. 30, 2012, U.S. patentapplication Ser. No. 13/584,618, filed Aug. 13, 2012 and U.S. patentapplication Ser. No. 13/621,530, filed Sep. 17, 2012. The disclosures ofthese applications are incorporated by reference in their entirety forall purposes.

TECHNICAL FIELD

This application relates generally to implantable stimulators.

BACKGROUND

Modulation of excitable tissue in the body by electrical stimulation hasbecome an important type of therapy for patients with chronic disablingconditions, including chronic pain, problems of movement initiation andcontrol, involuntary movements, vascular insufficiency, heartarrhythmias and more. A variety of therapeutic intra-body electricalstimulation techniques can treat these conditions. For instance, devicesmay be used to deliver stimulatory signals to excitable tissue, recordvital signs, perform pacing or defibrillation operations, record actionpotential activity from targeted tissue, control drug release fromtime-release capsules or drug pump units, or interface with the auditorysystem to assist with hearing. Typically, such devices utilize asubcutaneous battery operated implantable pulse generator (IPG) toprovide power or other charge storage mechanisms.

SUMMARY

In one aspect, some implementations provide an implantable wirelesslypowered device that includes: one or more electrodes configured to applyone or more electrical pulses to an excitable tissue; and a firstantenna configured to: receive, from a second antenna and throughelectrical radiative coupling, an input signal containing electricalenergy, the second antenna being physically separate from theimplantable device; and one or more circuits electrically connected tothe first antenna, the circuits configured to: create the one or moreelectrical pulses suitable for stimulation of excitable tissue using theelectrical energy contained in the input signal; and supply the one ormore electrical pulses to the one or more electrodes, wherein theimplantable device is shaped and arranged for delivery into a patient'sbody through an introducer or a needle of 18 gauge or smaller.

Implementations may include the following features. The one or moreelectrodes may include at least one recording electrode configured tosense neural activity of the subject. The one or more circuits may befurther configured to generate a recorded electrical signal encoding thesensed neural activity. The first antenna may be further configured totransmit the recorded electrical signal to the second antenna using theelectrical energy contained in the input signal.

The electrodes may include two (2) to twenty four (24) electrodes, eachhaving a longitudinal length between 0.25 and 6.0 mm and a diameterbetween 0.1 and 0.8 mm. The electrodes are spaced between 1 mm to 6 mmapart and have a combined surface area of between 0.06 mm² to 60.00 mm².The implantable device may be in a paddle style form factor. Theimplantable device may have a height between 0.1 mm and 0.8 mm, and awidth between 0.5 mm and 0.8 mm. The implantable device may be shapedconcavely to secure a lateral position on the excitable tissue after theimplantable device has been delivered into the patient's body.

In another aspect, some implementations provide a device that includes astylet comprising a mating feature at a distal end thereof; and animplantable device with a cylindrical body comprising a mating featureat a proximal end thereof, the mating feature of the implantable deviceconfigured to mate with the mating feature of the stylet to form asubassembly; wherein the subassembly of the stylet and implantabledevice with a cylindrical body is sized and shape for delivery into asubject's body through an introducer or needle that is 18 gauge orsmaller.

Implementations may include one or more of the following features. Thestylet may include a placement stylet. The mating feature of the styletmay include a protrusion and the mating feature of the implantabledevice includes an indentation, the protrusion being configured to matewith the indentation. The stylet may include a suction stylet, thesuction stylet including an inner plunger in a shaft, a suction tip, andan air chamber between the suction tip and a distal end of the innerplunger. The stylet may mate with the implantable device when a slidingmotion of the inner plunger in the shaft creates a negative pressure inthe air chamber to engage the suction tip with the mating feature on theimplantable device.

In yet another aspect, some implementations may provide a method fortreating neurological pain, including: placing an introducer through anincision site on a patient, the introducer including a needle that is 18gauge or less; advancing a first implantable device to a target site inthe patient's body through the introducer and causing an electricalimpulse to be applied to one or more electrodes within the implantabledevice to modulate excitable tissue at the target site within thepatient's body.

Implementations may include one or more of the following features.Advancing the first implantable device may include: advancing awirelessly powered implantable device that includes: a first antennaconfigured to: receive, from a second antenna and through electricalradiative coupling, an input signal containing electrical energy, thesecond antenna being physically separate from the implantable device;and one or more circuits electrically connected to the first antenna,the circuits configured to: create the one or more electrical pulsessuitable for stimulation of the excitable tissue using the electricalenergy contained in the input signal; and supply the one or moreelectrical pulses to the one or more electrodes.

The method may further include mating the implantable device with astylet. Advancing the implantable device may include advancing theminiature implantable device mated with the stylet through theintroducer. Mating the implantable device with a stylet may includemating the miniature implantable device with a placement stylet. Matingthe implantable device with a stylet may include mating the implantabledevice with a suction stylet. The method may further include activatingthe suction stylet by pulling a plunger in the suction stylet to createa negative pressure in an air chamber of the suction stylet so that thesuction stylet is mated with the implantable device. Advancing theimplantable device may further include advancing the implantable devicemated with the suction stylet. The method may further includewithdrawing the implantable device mated with the suction stylet. Themethod may further include: advancing a second implantable device to thetarget site in the patient's body through the introducer; and causing asecond electrical impulse to be applied to one or more electrodes withinthe second implantable device to modulate one or more excitable tissueat the target site within the patient's body.

In one aspect, an implantable device or recording device includes anenclosure shaped and configured for percutaneous delivery into apatient's body through an introducer. The enclosure houses one or moreelectrodes configured to apply one or more electrical pulses to anexcitable tissue or record neural activity from tissue. The enclosurepreferably also houses a first antenna configured to receive, from asecond antenna through electrical radiative coupling, an input signalcontaining electrical energy. In the preferred embodiments, the secondantenna is physically separate from the wirelessly powered device andmay be positioned external to the patient's body. In some cases, thefirst antenna is a dipole antenna. The enclosure further includes one ormore circuits electrically connected to the first antenna and configuredto create the electrical energy contained in the input signal and tosupply the electrical energy to the one or more electrodes or tocircuits to enable the conversion of the recording signals from theelectrodes. The first antenna can also be configured to transmit thedata signals from the on-board diagnostics or recordings.

In one configuration, a portion of the enclosure may leave theelectrodes in a non-direct contact with the excitable tissue after theimplantable device has been delivered into the subject's body. Theenclosure can be semi-cylindrical in shape and the electrodes mayinclude at least one directional electrode that directs a current pathassociated with the one or more electrical pulses to a direction that issubstantially perpendicular to the neural tissue. The electrodes mayinclude a semi-cylindrical array of electrodes. The electrodes may bemade of at least one of platinum, platinum-iridium, gallium-nitride,titanium-nitride, iridium-oxide, or combinations thereof. The electrodesmay include between two (2) to twenty-four (24) electrodes, each havinga longitudinal length from between about 0.25 and 6.0 mm and a diameterfrom between about 0.1 and 0.8 mm. The electrodes are spaced betweenabout 0.25 mm to 6 mm apart and have a combined surface area frombetween about 0.06 mm² to 250.0 mm².

In another aspect, a method for treating a patient with a disorder orchronic condition comprises positioning a miniature device into thepatient's body. In certain cases, the device is advanced percutaneouslythrough a needle, such as, for example, a tuohy needle, no larger than18 gauge. The device may be delivered to excitable tissue innervated bycentral and peripheral nerves and their plexuses or downstream branchessuch as the cochlear, cranial, trigeminal, occipital, radius, ulnar,vagus, celiac, cervical, spinal, lumbar, sacral, sciatic, femoral, orbrachial nerves or deep brain structures, and cortical surfaces of thebrain containing sensory or motor nerves.

The enclosure may have an external coating of biocompatible polymer, thepolymer includes at least one of: polymethymethacrylate (PMMA),polydimethylsiloxane (PDMS), parylene, polyurethance,polytetrafluoroethylene (PTFE), or polycarbonate. The enclosure mayfurther have an external coating of silicone elastomer. The enclosurecan further house antenna coupling contacts, the antenna contacts beingelectrically connected to the antennas and the circuit and configured tocouple the antenna with the surrounding tissue. The antenna couplingcontacts can include from between two to eight antenna-coupling pairs.The antenna coupling contacts may be located proximal, relative to theelectrodes, in the enclosure. The antenna coupling contacts can eachhave a longitudinal length of between about 0.1 mm and 6.0 mm, and awidth of between about 0.1 mm to 0.8 mm. The antenna coupling contactscan be spaced between about 5 mm and 80 mm apart. At least one of theantennas can be constructed as a conductive trace contained on one ofthe circuits. At least one of the antennas can be fabricated as aconductive wire connected to one of the circuits. The circuits can beflexible circuits. The flexible circuits may be placed proximal,relative to the electrodes, in the enclosure.

In yet another aspect, a stylet is configured to aid in the surgicalplacement of a miniature device. The stylet fits through the innerdiameter of a tuohy needle no greater than 18 gauge, and may contain afeature for mating the stylet to a miniature implantable device. On thedistal tip of the stylet is a mating feature, which may besemi-spherical, and grips the miniature implantable device duringplacement. Other features may include alternative extruded shapes formating the stylet to the miniature device. The mating feature may onlyextrude from the distal tip of the stylet from between about 0.1 mm and1.0 mm and does not fill the body of the device. In some cases, the matebetween the miniature device and the stylet is active only during distaldirectional movement of the stylet. The stylet may have a longitudinallength of between about 50 mm and 177 mm. The stylet may have a diameterin the range from between about 0.1 mm and 0.9 mm. The stylet may bemade of a rigid biocompatible material such as stainless steel,titanium, nylon, or polyethylene. The mating feature may have a surfacematerial that allows for increased friction such as silicon orpolyurethane to improve the mate between the stylet and the miniaturedevice.

Some implementations of the stylet include a central lumen that containsa plunger used for creating a negative pressure port on the distal tip.The negative pressure port exits where the mating feature connects tothe miniature device. This suction stylet can grip the miniature deviceduring distal and proximal directional movement. The suction stylet mayhave a locking feature that allows for the plunger pressure level to bemaintained without the operator maintaining the force on the plunger.

Some implementations provide a method of treating neurological pain. Themethod may include providing a miniature device including: an enclosurethat houses one or more electrodes; a first antenna configured toreceive, from a second antenna and through electrical radiativecoupling, an input signal containing electrical energy, the secondantenna being physically separate from the implantable device; one ormore flexible circuits electrically connected to the first antenna, theflexible circuits configured to convert the electrical energy containedin the input signal to a power source to supply energy to one or moreelectrodes, or to power recording circuitry connected to one or morerecording electrodes; and implanting the device into a subject's bodythrough an introducer.

In another aspect, a system for stimulating excitable tissue includes acontroller module having a first antenna external to the patient's bodyand configured to send an input signal containing electrical energy to asecond antenna through electrical radiative coupling. The second antennais a dipole antenna and is located in an enclosure in a miniaturedevice, such as those described above. The miniature device may notinclude an internal power source. The circuits of the device may includeonly passive components. The input signal has a carrier frequency in therange of about 300 MHz to about 8 GHz, preferably between about 750 MHzto about 2.8 GHz.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a miniature implantable deviceincluding wireless power receiving electronics.

FIG. 2 shows three different sized miniature implantable devices.

FIG. 3 illustrates a miniature implantable device entering an introducerneedle.

FIG. 4A shows a placement stylet capable of mating with a miniatureimplantable device.

FIG. 4B illustrates a miniature implantable device mated with aplacement stylet.

FIG. 5A shows a miniature implantable device mated with a placementstylet entering a proximal opening of an introducer needle.

FIGS. 5B and 5C show a miniature implantable device mated with aplacement stylet exiting a distal tip of an introducer needle.

FIG. 6 illustrates the anatomical placement of four miniatureimplantable devices in the forearm.

FIG. 7A illustrates an example suction stylet in zero pressure mode.

FIG. 7B illustrates the example suction stylet in first level ofnegative pressure mode.

FIG. 7C illustrates the example suction stylet in second level ofnegative pressure mode.

FIG. 7D illustrates an example miniature implantable device when thesuction stylet is not active.

FIG. 7E illustrates an example miniature implantable device when thesuction stylet is active.

FIG. 8A illustrates a miniature implantable device with multiplerecording or stimulating cylindrical electrode pads (eight shown).

FIG. 8B illustrates various electrode configurations for stimulation andor recording electrodes on the miniature implantable device body, withvarious inter-electrode spacing options and mixture of recording andstimulation electrode assignments.

FIG. 8C is a cutout view of a miniature implantable device withstimulation or recording electrodes and the electronic circuitry andwireless power receiver.

FIG. 9 illustrates a view of a miniature implantable device and a plateelectrode configuration for the stimulation or recording pads.

FIG. 10 depicts a high-level diagram of an example of a wireless neuralstimulation system.

FIG. 11 depicts a detailed diagram of an example of a wireless neuralstimulation system.

DETAILED DESCRIPTION

In various implementations, an implanted neural stimulation device cansend electrical stimulation to targeted excitable tissue by usingelectrical energy received without the use of cables or inductivecoupling. In particular, remote radio frequency (RF) energy can betransmitted and used to provide power to the implanted device. Theimplanted device can be used in the treatment of pain or a variety ofother modalities. The device may be placed nearby excitable tissueinnervated by central and peripheral nerves and their plexuses ordownstream branches (such as, for example, the cochlear, cranial,trigeminal, occipital, radius, ulnar, vagus, celiac, cervical, spinal,lumbar, sacral, sciatic, femoral, or brachial nerves or deep brainstructures, and cortical surfaces of the brain containing sensory ormotor nerves).

The implantable device includes an enclosure that houses one or moreconductive antennas (for example, dipole or patch antennas), internalelectronic circuitry for waveform and electrical energy rectification,and one or more electrode pads allowing for neural stimulation ofexcitable tissue or recording of neural activity in a surroundingtissue.

Various implementations can include distinct advantages over wired leadsin regards to ease of insertion, cross connections, elimination ofextension wires, and no requirement for an implantable pulse generatorin order to administer a chronic therapy. Various implementations alsomay have an associated lower overall cost compared to existingimplantable neural modulation systems due to the elimination of theimplantable pulse generator and this may lead to wider adoption ofneural modulation therapy for patients as well as reduction in overallcost to the healthcare system.

FIG. 1 illustrates an example miniature implantable device 100. Theimplantable device 100 includes a body 116 with a distal end 114 and aproximal end 112.

The distal end 114 includes a rounded tip 102. The distal end 114 of theminiature wireless device body 116 may include a non-conductive tip 102that is rounded with a length of between about 0.5 mm and about 1.0 mm,with a smooth finish for navigating the device through tissue.

The device body 106 includes electrodes 104 and houses electroniccircuitry 106. In some implementations, the miniature implantable devicemay have between one and twenty-four cylindrical electrodes 104 on itsdistal end 114 with a diameter between about 0.1 mm and about 0.8 mm forstimulation applications. The diameters and other sizes may, of course,vary from one target treatment to another target treatment. Theelectrodes 104 may have a longitudinal length of between about 0.25 mmand about 6.0 mm from the distal end 114 toward the proximal end 112.The spacing between the electrode contacts may be between about 0.25 mmand about 6.0 mm. The total electrode surface area of the cylindricalwireless lead body may be between about 0.06 mm² and about 250.0 mm².

The proximal end 112 includes a suturing feature 108 and a matingfeature 110. The suturing feature 108 is a passage through the proximalend with a central axis that is parallel to a longitudinal axis of thedevice body 106. Suturing feature 108 may allow a clinician to sutureand anchor implantable device 100 during an implantation procedure. Forinstance, suture can be passed through the passage of suturing feature108 and tied to tissue. In some cases, the implantable device 100 can besutured to the surrounding tissue. Suturing the implantable device mayreduce mobility and improve stability of the implanted device.

Mating feature 110 may allow the device 100 to be mechanically matedwith a stylet, as disclosed herein. In one configuration, mating feature110 is a concave indentation that extends along a longitudinal axis ofthe device body 106 from the proximal end 112. The concave indentationmates with a corresponding feature on a placement stylet or suctionstylet. The concave stylet-mating feature on the proximal end 110 ofimplantable device 100 can have, for example, a length of between about0.1 mm and 1.0 mm. In other configurations, the stylet-mating feature110 may be semi-spherical or asymmetrical in shape for improvedsteerability of the device during implantation.

The various devices described herein, including device 100, may include,for example, anywhere from one to twenty-four electrodes 104, any ofwhich can be designated by a programmer user as either a cathode or ananode. For example, electrodes 104 can include multiple cathodes coupledto the targeted tissue as well as at least one anode. The electrodearray can receive electrical stimulation pulses ranging from about 0 toabout 10 V peak amplitude at a pulse width up to about 1 millisecond.Such stimulation pulses may be from a single receiver element within thedevice body. The polarity of the electrodes can produce various volumeconduction distributions from the cathodes to the anodes to inhibit orexcite surrounding excitable tissue, which may include A-δ and/orprimary or secondary c-fiber afferents. To reduce electrode impedance,the electrodes may be made of a conductive, corrosion resistant,biocompatible material such as, for example, platinum, platinum-iridium,gallium-nitride, titanium-nitride, or iridium-oxide.

The miniature implantable device 100 may be 0.8 mm diameter or smaller.Miniature implantable device 100 may receive microwave or RF energy froman external source non-inductively and without a wire. The miniatureimplantable 100 device may contain the circuitry necessary to receivethe pulse instructions from a source external to the body.

In particular, electronic circuitry 106 of the miniature implantabledevice may convert an input signal received at the one or more antennasinto an electrical energy and electrical pulses. In someimplementations, extension tubing can provide an enclosure that houses,for example, flex circuitry. In some embodiments, the electroniccircuitry 106 may include one or a plurality of diodes that function torectify the wireless signal, such as a sinusoidal signal, picked up bythe non-inductive antenna(s). The diodes have a low threshold voltage tomaximize the energy used for creating waveforms and power. Additionally,internal circuitry 106 may include a charge balancing microelectroniccomponent to reduce or prevent corrosion as well as a current limiter.

In certain embodiments, the electronic circuitry 106 may include one ormore non-inductive antennas, a rectifier, a charge balancer, a currentlimiter, a controller, and a device interface. In brief, the rectifierfunctions to rectify the signal received by the one or morenon-inductive antennas. The rectified signal may provide power toelectrodes 104. The rectified signal may also be fed to a charge balancecomponent that is configured to create one or more electrical pulsessuch that the one or more electrical pulses result in a substantiallyzero net charge (that is, the pulses are charge balanced). The chargebalanced pulses are passed through the current limiter to the electrodeinterface, which applies the electrical pulses to electrodes 104.

In some implementations, an internal dipole (or other) antennaconfiguration(s) may be used in lead 100 to receive RF power throughelectrical radiative coupling. This coupling mechanism can allow suchdevices to produce electrical currents capable of stimulating nervebundles without a physical connection to an implantable pulse generator(IPG) or use of an inductive coil. In some implementations, between twoto eight tissue-exposed-ring-antenna coupling contacts may be proximalto the electrodes. The tissue-exposed-ring-antenna coupling contacts mayhave a longitudinal length of between about 0.25 mm and about 6.0 mmfrom the distal end 114 toward the proximal end 110. The spacing betweenthe tissue-exposed ring antenna coupling contacts may be between about 5mm and about 80 mm. In certain implementations,tissue-exposed-small-antenna coupling contacts with a diameter betweenabout 0.2 mm and about 0.6 mm may be used in lieu of thetissue-exposed-ring-antenna coupling contacts.

In some implementations, at least one of the antennas can be constructedas a conductive trace feature contained on one of the circuits. In otherimplementations, at least one of the antennas can be fabricated as aconductive wire connected to one of the circuits. In variousimplementations, implantable device 100 my employ non-inductive, forexample, dipole or other antenna configuration(s), to receive RF powerthrough electrical radiative coupling.

For context, neural stimulating devices may utilize a battery-powered orcharge-storage component. Such devices are no longer functional once thebattery cannot be recharged or charge cannot be stored. Consequently,for an implanted device, a patient would need to undergo a subsequentsurgical procedure to obtain a functional replacement device.

In contrast, some implementations disclosed herein do not rely uponbattery power or charge storage for operation. In some configurations,the implantable device can receive electrical power from radiated RFenergy non-inductively and without a wired connection. As a result, thelife of an implanted device is no longer limited by the life of thebattery or ability to store charge.

Further, the electrical radiative coupling mechanism (for example, adipole antenna) can be utilized to improve the form factor of theminiature implanted device and allow for miniature diameters. Electricalradiative coupling may also allow for the transmission and reception ofenergy at greater depths with less degradation in efficiency thaninductive coil techniques. This electrical radiative coupling canprovide an advantage over devices that employ inductive coupling wherethe efficiency of such implants may be highly dependent on the distanceseparating the external transmitter coil and the implanted receivercoil.

Accordingly, some implementations disclosed herein do not includeinductive loops to receive RF energies in a wireless manner. Instead,some implementations disclosed herein use electric radiative coupling toreceive RF energies. Such implementations facilitate a smaller formfactor for a fully functional implantable electrical stimulation orrecording device. The improved form factor may result in a less invasivesurgical procedure for placement of the device. The improved form factormay also decrease scarring the amount of bodily tissue in contact withthe implanted device is reduced.

A telemetry signal may be transmitted by the miniature implantabledevice 100 to deliver information to an external controller. Thetelemetry signal may be sent by modulation of a carrier signal. Thetelemetry signal does not interfere with the input received to power theminiature implantable device. In one example, the telemetry signal andpowering signal are combined into one signal, where the RF telemetrysignal is used to modulate the RF powering signal, and thus theimplanted device is powered directly by the received telemetry signal;separate electronic subsystems harness the power contained in the signaland interpret the data content of the signal. In other embodiments, thetelemetry output rate is at least 8 kilobits per second.

In other implementations, a RF pulse generator system, locatedexternally to the miniature implanted device 100, may store parametersdefining the excitation pulses to be applied at electrodes 104, whichare transmitted via the second antenna.

FIG. 2 illustrates three examples of miniature implantable devices 200A,200B, and 200C with various diameters. Miniature implantable device 200Ais a miniature implantable device with a diameter of 0.8 mm. Miniatureimplantable device 200A includes a suturing feature 208A to allow aclinician to suture and anchor implantable miniature implantable device200A during an implantation procedure. For instance, suture can bepassed through the passage of suturing feature 208A and tied to tissuesuch that the mobility of the implanted device is reduced. Asillustrated, implantable device 200A also includes an indentation 210Aon the proximal end to allow for mating with a placement stylet duringimplantation.

Miniature implantable device 200B has a diameter of 0.4 mm and has asuturing feature 208B similar to 208A. Implantable device 200B alsoincludes an indentation 210B on the proximal end to allow for matingwith a placement stylet during implantation.

Miniature implantable device 200C has a diameter of 0.1 mm. Miniatureimplantable device 200C includes a suturing feature 208C in the form ofribs to aid suture in attaching to a surrounding tissue. Implantabledevice 200C also may include an indentation 210C to allow for matingwith a placement stylet during implantation.

FIG. 3 illustrates the miniature wireless device 100 (e.g., a 0.8 mmdiameter) entering an 18 gauge needle 300. The distal end (not shown) ofminiature implantable device is in position to enter the proximalopening 302 of an 18-gauge needle 300. Miniature implantable device 100has a diameter small enough to fit into the inner lumen 304 of theneedle 300. The illustration may correspond to an implantation of aminiature implantable device with a diameter of 0.8 mm, shown as theimplantable device 200A in FIG. 2. Notably, the middle and bottomdevices (0.4 mm and 0.1 mm, respectively) shown in FIG. 2 are sized foradvancement through introducer needles with even smaller sizes, (e.g.,22 gauge or smaller).

While it is possible to place the device 100 directly into an introducerneedle, doing so may not be desirable as the implantable deviceenclosure may not be as rigid as a guide wire and may not slide easilywithin the inner lumen of the introducer needle. Yet, a guide wire maynot be used because the implantable device may not have a central voidthrough which to mount the guide wire. To improve the ease of placementthrough an introducer needle, a stylet may be used to provide somerigidity to the miniature device.

FIG. 4A shows a placement stylet 400 capable of mating with a miniatureimplantable device 100 according to some implementations. Placementstylet 400 includes a distal end 408, device body 404, and proximal end410. Distal end 408 includes a mating feature 402 to allow the placementstylet 400 to engage, for example, miniature implantable device 100. Themating feature 402 is, for example, a convex protrusion that is shapedand sized to mate with the concave indentation 110 of the lead 100.Proximal end 406 includes handle 406 for operator to hold placementstylet 400, for example, during an implantation procedure. Placementstylet 400 can have a longitudinal length of between about 50 mm andabout 177 mm. Placement stylet 400 can have an outer diameter in therange from between about 0.1 mm and about 0.9 mm. Placement stylet 400may be made of a rigid biocompatible material such as stainless steel,titanium, nylon, or polyethylene.

FIG. 4B illustrates a miniature implantable device 100 mated with aplacement stylet 400. A clinician may mate the miniature implantabledevice 100 onto the placement stylet 400. The mating feature 402 on thedistal end 408 of the stylet may mate with mating feature 110 on theproximal end 112 of miniature implantable device 100. Mating feature 402on placement stylet 400 may be semi-spherical in shape, and may providemechanical gripping for placement stylet 400 to engage the miniatureimplantable device 100 during placement. Mating feature 402 may becomplementary in shape to the shape of mating feature 112 on theproximal end 110 of the device 100. In some configurations, matingfeature 402 may be convex in shape. In other configurations, matingfeature 402 may include extruded shapes for mating the stylet 400 to theminiature implantable device 100 at mating feature 112, which may have asquare, hexagon, star, or an asymmetrical shape. Mating feature 402 mayonly protrude from the distal end 408 of placement stylet 400 frombetween 0.1 mm and 1.0 mm and may not fill the entirety of the devicebody 106 (that is, the feature 402 may only extend partially into devicebody 106). Mating feature 402 may have a surface material that allowsfor increased friction to improve the mate between placement stylet 400and the miniature implantable device 100. Example materials may includesilicon or polyurethane.

FIG. 5A illustrates a miniature implantable device 100 mated with aplacement stylet 400 entering a proximal opening 302 of needle 300.Miniature implantable device 100 includes lead body 116 that includeselectrodes 104 and houses electronic circuitry 106. The proximal end 112of miniature implantable device 100 is now mated with the distal end 408of placement stylet 400. As illustrated, after the miniature implantabledevice 100 has been mated to placement stylet 400, the subassembly ofthe device 100 with the stylet 400 can now be inserted into an 18 gaugeneedle 300 or smaller. In particular, the miniature implantable device100 at the proximal opening 302 of needle 300 is being pushed intoposition with the placement stylet 400. In fact, the stylet/miniaturedevice subassembly may now slide freely within the inner lumen 304 ofthe needle 300. The free sliding motion may aid in the surgicalplacement of the miniature device 100.

FIGS. 5B and 5C show a miniature implantable device 100 mated with aplacement stylet 400 exiting a distal end 502 of needle 300. Asdiscussed above, the miniature implantable device 100 may freelytraverse the inner lumen 304 of needle 300 with a size of 18 gauge orsmaller. Once the traversal is completed, the miniature implantabledevice 100 may exit the needle under the pushing force applied on theplacement stylet 400 mated to the device 100. As illustrated, roundedtip 102 and body 116 of miniature implantable 100 have exited the distalend 502 of needle 300. The portions of body 116 that include electrodes104 and electronic circuitry 106 are also shown on FIGS. 5B-5C. Theproximal end 112 of miniature implantable 100 is mated to the distal end408 of placement stylet 400. After the implantable 100 has been placedinto a target region, the implantable device 100 may be sutured oranchored in place. Thereafter, the placement stylet 400 may be unmatedfrom the implanted 100. A clinician may then withdraw the placementstylet 400 by pulling the placement stylet 400 out of the patient's bodythrough the needle 300. The placement and withdrawal process may beperformed under imaging guidance, such as, for example, X-Rayfluoroscopy, ultrasound fluoroscopy, etc. Once the procedure iscompleted, needle 300 may be removed.

FIG. 6 demonstrates the feasibility of placing multiple miniatureimplantable devices in the anatomical positions of the forearm. Thecompact size of the miniature implantable device 100 may allow minimallyinvasive placement procedure, thereby reducing complications duringprocedure and improving recovery time after procedure. Moreover, thecompact size may allow multiple miniature implantable devices to beplaced in nearby target areas. As shown in FIG. 6, four miniatureimplantable devices 100 are placed into the forearm of a patient, one inthe upper forearm area and three in the lower forearm area. Eachimplanted lead may treat a specific nerve branch in the forearm region.Similarly, the miniature implantable devices 100 also may be deliveredto treat a neural tissue branching from the spinal column including butnot limited to the dorsal root ganglia, traversing, or exiting nerve.The miniature implantable devices 100 may also be delivered to treatperipheral nerve targets such as the radius, ulnar, sciatic, femoral,occipital, or brachial nerves. Given the compact size of the miniatureleads, two or more such devices may be placed with pin-point precisionto treat multiple nerve branches or peripheral nerve targets at the sametime. In particular, two or more such devices may be placed with closeproximity within a target area to provide pain-relief therapy to one ormore excitable tissues within the target area. For instance, a patientmay have one miniature implantable device 100 implanted adjacent to ornear a target area. If more therapeutic effect is desired, the patientmay have additional miniature implantable devices 100 implanted adjacentto or near the target area to enhance the therapeutic effect.

FIGS. 7A-7E illustrate a suction stylet 700 in various modes ofoperation. The suction stylet 700 is different from the placement stylet400 described above. As shown in FIG. 7A, the suction stylet 700 ishollow inside and may have an outer diameter of between about 0.1 mm and0.9 mm and may have a longitudinal length of between about 50 mm and 170mm. The suction stylet 700 may have an inner diameter between about 0.05mm and 0.75 mm. The suction stylet 700 includes distal end 718, styletbody 714, and proximal end 716.

The distal end 718 may include a mating feature 702, chamber 704, andplunger tip 706. Mating feature 702 also may be referred to as thesuction tip. In some configurations, mating feature 702 may besemi-spherical in shape and may have a diameter between about 0.05 mmand 0.08 mm. Mating feature 702 on suction stylet 700 may mate to matingfeature 110 on miniature wireless lead 100, in a manner similar to themechanical mating described above. In some instances, a mating force maybe provided by a negative air pressure created inside air chamber 704 onsuction stylet 700. In particular, by moving the plunger tip 706 alongthe shaft for inner plunger 708, a negative air pressure may be createdin chamber 704.

Stylet body 714 may include inner plunger 708 located inside shaft 722.The inner plunger shaft 722 may have a diameter between about 0.05 mmand 0.75 mm, allowing the plunger 708 to slide inside of the hollowsuction stylet 700. The total length of the inner plunger including theinner plunger handle may be between about 50 mm and 170 mm. The innerplunger shaft, when installed, may not protrude beyond the suction tip.

The proximal end 720 of suction stylet 700 may include base 716, handle712, and locking feature 710. Base 716 may have a diameter of betweenabout 0.1 mm and 0.9 mm depending on the outer diameter of the hollowstylet 700 being utilized. Handle 712 may include cap 712 a and tip 712b. Cap 712 a closes the tubing of suction stylet 700. Handle tip 712 bmay be pulled out during a placement procedure. The pulling may causesliding motion of the plunger 708 inside shaft 722, which creates anegative air pressure in chamber 704. Suction force may be created onsuction tip, mating feature 702, so that suction stylet 700 is matedwith miniature implantable device 100. Locking mechanism 710 may includespike 710 a, spike 710 b, and hinge 710 c. Hinge 710 c is mounted onbase 716 and may rotate to engage spikes 710 a and 710 b with cap 712 a,as discussed below.

FIGS. 7A to 7C show the suction stylet without the mating miniatureimplantable device. As illustrated, the inner plunger 708 may be slid ina translating motion inside shaft 722 to different locations within thehollow stylet 700. Locking mechanism 710 may be used to lock plunger 708into certain positions.

In particular, FIG. 7A shows the inner plunger 708 in a complete seatedcondition with respect to the distal end 720 of stylet 700. In thisposition, no pressure differential may exist between the mating feature702 and plunger tip 706.

FIGS. 7B and 7D shows the inner plunger 708 at stage 1 position, whichmay be between about 1 mm and 10 mm from mating feature 702 (suctiontip) of the hollow stylet 700. FIG. 7B shows suction stylet 700 withoutthe mated miniature implantable device 100, while FIG. 7D shows suctionstylet 700 mated with miniature implantable device 100. By pulling thehandle tip 712 b away from the hollow stylet, a pressure differentialmay be generated to create a temporary mate between the miniatureimplantable device 100 and the stylet 100. The mate is between matingfeature 102 on miniature implantable device 100 and suction tip 702 onsuction stylet 700. Locking mechanism 710, as shown in FIG. 7B, may lockthe inner plunger 708 in place by engaging spike 710 a between base 716and cap 712 a. Once locked, the pressure differential between suctiontip (mating feature 702) and plunger tip 706 may be maintained. Thislocking mechanism may be adjustable to allow for the inner plunger to belocked in a desired location.

FIGS. 7C and 7E illustrate the inner plunger 708 being locked into astage 2 location, which may be between about 2 mm and 30 mm from matingfeature 702 (suction tip) of the hollow stylet 700. FIG. 7C showssuction stylet 700 without the mated miniature implantable device 100,while FIG. 7E shows suction stylet 700 mated with miniature implantabledevice 100. This stage may have a greater pressure differentialgenerated than the stage 1 location depicted in FIG. 7B. In otherexamples, a suction stylet assembly may have one more locking stagesdepending on the locking mechanism utilized. An adjustable lockingmechanism may allow for infinite locking distance locations.

The suction stylet design may provide the clinician the ability toinstall and remove the miniature implantable device 100 from a patient.As discussed above, once suction stylet 700 is activated to engageminiature implantable device 100, an assembly of miniature implantabledevice 100 and suction stylet 700 may be created. The clinician may pushthe suction stylet to advance the entire assembly, for example, down theinner lumen 304 of needle 300, towards the target site. If the miniatureimplantable device 100 is already implanted, the clinician can mate theminiature implantable device 100 to the suction tip of the stylet 700,then pull on handle tip 712 b. Plunger 708 may slide inside shaft 722,thereby creating a pressure differential between suction tip 702 andplunger tip 706. The pressure differential may engage the miniatureimplantable device 100, and the clinician may withdraw the suctionstylet 700 to take the implanted lead 100 from within the patient.

FIG. 8A shows cylindrical electrodes 804 (eight (8) shown) on theoutside of a lead 800. The outer diameter of lead 800 may be 0.8 cm orsmaller. Each cylindrical electrode 804 may operate as a recording orstimulating electrode. A stimulating electrode may apply electric pulsesto an excitable tissue to achieve therapeutic effect. A recordingelectrode may record or sense neural activity from surrounding tissue.In some instances, the electrodes may alternate between stimulating andrecording electrodes. In the example shown, the miniature lead 800 isnot tethered and not connected to another structure or device formechanical or electrical interface. One or more electrical flexcircuitry may be internal to the miniature lead. The flex circuit may beinside gaps 806, in between electrodes 804. Lead 800 may also include arounded-tip 802 for easy placement, as well as a mating feature to matethe lead 800 with a stylet, such as those described above.

FIG. 8B shows four example miniature implantable devices incorporatingmultiple recording and/or stimulating electrodes 804. The four exampleleads shown do not have an inner stylet lumen to mount a stylet or aguide wire, but may include a mating feature such as those describedabove. The recording and/or stimulating electrode pads 804 may couple toa surrounding tissue for recording and/or stimulating. In a recordingmode, neural activities of the surrounding tissue may be sensed andcapture in electrical signals that encode such neural activities. In astimulating mode, electric pulses may be applied to the surroundingtissue for pain relief. In some configurations, the electric circuitrymay be spaced in between the recording and/or stimulating electrodepads, for example, in gaps 806. As illustrated, example miniatureimplantable devices 800 may include rounded tip 802 for easy placement.

FIG. 8C illustrates a miniature implantable device 800 with stimulatingand/or recording electrodes 804 located at the distal end of the lead,in the direction of the rounded tip 802. As illustrated, the electroniccircuitry 808 is located towards the proximal end of implantable device800, rather than spaced between the electrodes 802.

For the configurations shown in FIGS. 7A to 7C, the electronic circuitrymay provide power to drive the stimulating and/or recording electrodes.As described above, the electric pulses may be created by the electroniccircuitry based on the input signal received at the antennas on theimplantable devices. The electric pulses may be sent to a stimulatingelectrode to delivery pain-relief to an excitable tissue. As discussedabove, a recording electrode may record neural activities of asurrounding tissue. The electronic circuitry also may route the recordedanalog signal to the antennas on the implantable device which may inturn transmit the recorded analog signal to an external controller,located outside the patient body. In some implementations, the recordedanalog signal may be processed and transmitted in a manner similar tothe telemetry signal described above. For example, the transmission ofthe recorded analog signal, like the telemetry signal discussed herein,may be powered by the electrical power in the input signal.

FIG. 9 depicts an example of a lead 900 with each electrode pad 902configured as a rectangular square. As illustrated, each rectangularsquare electrode pad 902 may include an electrode 906. Electroniccircuitry may be located on structures 904. Electrode 906 may have asurface area of at least 0.06 mm². This implantable device 900 may havea total width from between about 0.5 mm and 0.8 mm. The height of theimplantable device 900 may be from between about 0.1 mm and about 0.8mm. The total length of the implantable device 900 may be from betweenabout 10 mm and about 600 mm. The rectangular electrode pads 902 mayhave a length from between about 0.5 mm and about 6.0 mm and a widthfrom between about 0.45 mm and about 0.75 mm. The inter-electrodespacing may be from between about 0.1 mm and about 6.0 mm. Thisimplantable device 900 may be suitable for stimulating a relativelylarge area.

FIGS. 10 and 11 illustrate an example of a neural stimulation systemthat may employ the implantable devices described above. Theseimplantable devices may also be referred to as implantable leads.

In particular, FIG. 10 depicts a high-level diagram of an example of aneural stimulation system. The neural stimulation system may includefour major components, namely, a programmer module 1002, a RF pulsegenerator module 1006, a transmit (TX) antenna 1010 (for example, apatch antenna, slot antenna, or a dipole antenna), and an implanteddevice 1014, which may be a lead such as those described above. Theprogrammer module 1002 may be a computer device, such as a smart phone,running a software application that supports a wireless connection 1014,such as Bluetooth®. The application can enable the user to view thesystem status and diagnostics, change various parameters,increase/decrease the desired stimulus amplitude of the electrodepulses, and adjust feedback sensitivity of the RF pulse generator module1006, among other functions.

The RF pulse generator module 1006 may include communication electronicsthat support the wireless connection 1004, the stimulation circuitry,and the battery to power the generator electronics. In someimplementations, the RF pulse generator module 1006 includes the TXantenna embedded into its packaging form factor while, in otherimplementations, the TX antenna is connected to the RF pulse generatormodule 1006 through a wired connection 1008 or a wireless connection(not shown). The TX antenna 1010 may be coupled directly to tissue tocreate an electric field that powers the implanted device 1014. The TXantenna 1010 communicates with the implanted device 1014 through an RFinterface. For instance, the TX antenna 1010 radiates an RF transmissionsignal that is modulated and encoded by the RF pulse generator module1010. The implanted device 1014 contains one or more antennas, such asdipole antenna(s), to receive and transmit through RF interface 1012. Inparticular, the coupling mechanism between antenna 1010 and the one ormore antennas on the implanted device 1014 is electrical radiativecoupling and not inductive coupling. In other words, the coupling isthrough an electric field rather than a magnetic field.

Through this electrical radiative coupling, the TX antenna 1010 canprovide an input signal to the implanted device 1014. This input signalcontains energy and may contain information encoding stimulus waveformsto be applied at the electrodes of the implanted device 1014. In someimplementations, the power level of this input signal directlydetermines an applied amplitude (for example, power, current, orvoltage) of the one or more electrical pulses created using theelectrical energy contained in the input signal. Within the implanteddevice 1014 are components for demodulating the RF transmission signal,and electrodes to deliver the stimulation to surrounding neuronaltissue.

The RF pulse generator module 1006 can be implanted subcutaneously, orit can be worn external to the body. When external to the body, the RFgenerator module 1006 can be incorporated into a belt or harness designto allow for electric radiative coupling through the skin and underlyingtissue to transfer power and/or control parameters to the implanteddevice 1014, which can be a passive stimulator. In either event,receiver circuit(s) internal to the device 1014 can capture the energyradiated by the TX antenna 1010 and convert this energy to an electricalwaveform. The receiver circuit(s) may further modify the waveform tocreate an electrical pulse suitable for the stimulation of neuraltissue, and this pulse may be delivered to the tissue via electrodepads.

In some implementations, the RF pulse generator module 1006 can remotelycontrol the stimulus parameters (that is, the parameters of theelectrical pulses applied to the neural tissue) and monitor feedbackfrom the wireless device 1014 based on RF signals received from theimplanted wireless device 1014. A feedback detection algorithmimplemented by the RF pulse generator module 1006 can monitor data sentwirelessly from the implanted wireless device 1014, includinginformation about the energy that the implanted wireless device 1014 isreceiving from the RF pulse generator and information about the stimuluswaveform being delivered to the electrode pads. In order to provide aneffective therapy for a given medical condition, the system can be tunedto provide the optimal amount of excitation or inhibition to the nervefibers by electrical stimulation. A closed loop feedback control methodcan be used in which the output signals from the implanted wirelessdevice 1014 are monitored and used to determine the appropriate level ofneural stimulation current for maintaining effective neuronalactivation, or, in some cases, the patient can manually adjust theoutput signals in an open loop control method.

FIG. 11 depicts a detailed diagram of an example of the neuralstimulation system. As depicted, the programming module 1002 maycomprise user input system 1102 and communication subsystem 1108. Theuser input system 1121 may allow various parameter settings to beadjusted (in some cases, in an open loop fashion) by the user in theform of instruction sets. The communication subsystem 1108 may transmitthese instruction sets (and other information) via the wirelessconnection 1004, such as Bluetooth or Wi-Fi, to the RF pulse generatormodule 1006, as well as receive data from module 1006.

For instance, the programmer module 1002, which can be utilized formultiple users, such as a patient's control unit or clinician'sprogrammer unit, can be used to send stimulation parameters to the RFpulse generator module 1006. The stimulation parameters that can becontrolled may include pulse amplitude, pulse frequency, and pulse widthin the ranges shown in Table 1. In this context the term pulse refers tothe phase of the waveform that directly produces stimulation of thetissue; the parameters of the charge-balancing phase (described below)can similarly be controlled. The patient and/or the clinician can alsooptionally control overall duration and pattern of treatment.

TABLE 1 Stimulation Parameter Pulse Amplitude: 0 to 20 mA PulseFrequency: 0 to 20,000 Hz Pulse Width: 0 to 2 ms

The implantable device 1014 or RF pulse generator module 1014 (which maybe a lead such as those described above) may be initially programmed tomeet the specific parameter settings for each individual patient duringthe initial implantation procedure. Because medical conditions or thebody itself can change over time, the ability to re-adjust the parametersettings may be beneficial to ensure ongoing efficacy of the neuralmodulation therapy.

The programmer module 1002 may be functionally a smart device andassociated application. The smart device hardware may include a CPU 1106and be used as a vehicle to handle touchscreen input on a graphical userinterface (GUI) 1104, for processing and storing data.

The RF pulse generator module 1006 may be connected via wired connection1008 to an external TX antenna 1010. Alternatively, both the antenna andthe RF pulse generator are located subcutaneously (not shown).

The signals sent by RF pulse generator module 1006 to the implanteddevice 1014 may include both power and parameter-setting attributes inregards to stimulus waveform, amplitude, pulse width, and frequency. TheRF pulse generator module 1006 can also function as a wireless receivingunit that receives feedback signals from the implanted device 1014. Tothat end, the RF pulse generator module 1006 may containmicroelectronics or other circuitry to handle the generation of thesignals transmitted to the device 1014 as well as handle feedbacksignals, such as those from the device 1014. For example, the RF pulsegenerator module 1006 may comprise controller subsystem 1114,high-frequency oscillator 1118, RF amplifier 1116, a RF switch, and afeedback subsystem 1112.

The controller subsystem 1114 may include a CPU 1130 to handle dataprocessing, a memory subsystem 1128 such as a local memory,communication subsystem 1134 to communicate with programmer module 1002(including receiving stimulation parameters from programmer module),pulse generator circuitry 1136, and digital/analog (D/A) converters1132.

The controller subsystem 1114 may be used by the patient and/or theclinician to control the stimulation parameter settings (for example, bycontrolling the parameters of the signal sent from RF pulse generatormodule 1006 to device 1014). These parameter settings can affect, forexample, the power, current level, or shape of the one or moreelectrical pulses. The programming of the stimulation parameters can beperformed using the programming module 1002, as described above, to setthe repetition rate, pulse width, amplitude, and waveform that will betransmitted by RF energy to the receive (RX) antenna 1138, typically adipole antenna (although other types may be used), in the wirelessimplanted device 1114. The clinician may have the option of lockingand/or hiding certain settings within the programmer interface, thuslimiting the patient's ability to view or adjust certain parametersbecause adjustment of certain parameters may require detailed medicalknowledge of neurophysiology, neuroanatomy, protocols for neuralmodulation, and safety limits of electrical stimulation.

The controller subsystem 1114 may store received parameter settings inthe local memory subsystem 1128, until the parameter settings aremodified by new input data received from the programming module 1002.The CPU 1106 may use the parameters stored in the local memory tocontrol the pulse generator circuitry 1136 to generate a stimuluswaveform that is modulated by a high frequency oscillator 1118 in therange from 300 MHz to 8 GHz. The resulting RF signal may then beamplified by RF amplifier 1126 and then sent through an RF switch 1123to the TX antenna 1010 to reach through depths of tissue to the RXantenna 1138.

In some implementations, the RF signal sent by TX antenna 1010 maysimply be a power transmission signal used by the device 1014 togenerate electric pulses. In other implementations, a telemetry signalmay also be transmitted to the device 1014 to send instructions aboutthe various operations of the device 1014. The telemetry signal may besent by the modulation of the carrier signal (through the skin ifexternal, or through other body tissues if the pulse generator module1006 is implanted subcutaneously). The telemetry signal is used tomodulate the carrier signal (a high frequency signal) that is coupledonto the implanted antenna(s) 1138 and does not interfere with the inputreceived on the same lead to power the implant. In one embodiment thetelemetry signal and powering signal are combined into one signal, wherethe RF telemetry signal is used to modulate the RF powering signal, andthus the implanted stimulator is powered directly by the receivedtelemetry signal; separate subsystems in the stimulator harness thepower contained in the signal and interpret the data content of thesignal.

The RF switch 1123 may be a multipurpose device such as a dualdirectional coupler, which passes the relatively high amplitude,extremely short duration RF pulse to the TX antenna 1010 with minimalinsertion loss while simultaneously providing two low-level outputs tofeedback subsystem 1112; one output delivers a forward power signal tothe feedback subsystem 1112, where the forward power signal is anattenuated version of the RF pulse sent to the TX antenna 1010, and theother output delivers a reverse power signal to a different port of thefeedback subsystem 212, where reverse power is an attenuated version ofthe reflected RF energy from the TX Antenna 1010.

During the on-cycle time (when an RF signal is being transmitted to thedevice 1014), the RF switch 1123 is set to send the forward power signalto feedback subsystem. During the off-cycle time (when an RF signal isnot being transmitted to the device 1014), the RF switch 1123 can changeto a receiving mode in which the reflected RF energy and/or RF signalsfrom the device 1014 are received to be analyzed in the feedbacksubsystem 1112.

The feedback subsystem 1112 of the RF pulse generator module 1006 mayinclude reception circuitry to receive and extract telemetry or otherfeedback signals from the device 1014 and/or reflected RF energy fromthe signal sent by TX antenna 1010. The feedback subsystem may includean amplifier 1126, a filter 1124, a demodulator 1122, and an A/Dconverter 1120.

The feedback subsystem 1112 receives the forward power signal andconverts this high-frequency AC signal to a DC level that can be sampledand sent to the controller subsystem 1114. In this way thecharacteristics of the generated RF pulse can be compared to a referencesignal within the controller subsystem 1114. If a disparity (error)exists in any parameter, the controller subsystem 1114 can adjust theoutput to the RF pulse generator 1006. The nature of the adjustment canbe, for example, proportional to the computed error. The controllersubsystem 1114 can incorporate additional inputs and limits on itsadjustment scheme such as the signal amplitude of the reverse power andany predetermined maximum or minimum values for various pulseparameters.

The reverse power signal can be used to detect fault conditions in theRF-power delivery system. In an ideal condition, when TX antenna 1010has perfectly matched impedance to the tissue that it contacts, theelectromagnetic waves generated from the RF pulse generator 1006 passunimpeded from the TX antenna 1010 into the body tissue. However, inreal-world applications a large degree of variability may exist in thebody types of users, types of clothing worn, and positioning of theantenna 1010 relative to the body surface. Since the impedance of theantenna 1010 depends on the relative permittivity of the underlyingtissue and any intervening materials, and also depends on the overallseparation distance of the antenna from the skin, in any givenapplication there can be an impedance mismatch at the interface of theTX antenna 1010 with the body surface. When such a mismatch occurs, theelectromagnetic waves sent from the RF pulse generator 1006 arepartially reflected at this interface, and this reflected energypropagates backward through the antenna feed.

The dual directional coupler RF switch 1123 may prevent the reflected RFenergy propagating back into the amplifier 1126, and may attenuate thisreflected RF signal and send the attenuated signal as the reverse powersignal to the feedback subsystem 1112. The feedback subsystem 1112 canconvert this high-frequency AC signal to a DC level that can be sampledand sent to the controller subsystem 1114. The controller subsystem 1114can then calculate the ratio of the amplitude of the reverse powersignal to the amplitude of the forward power signal. The ratio of theamplitude of reverse power signal to the amplitude level of forwardpower may indicate severity of the impedance mismatch.

In order to sense impedance mismatch conditions, the controllersubsystem 1114 can measure the reflected-power ratio in real time, andaccording to preset thresholds for this measurement, the controllersubsystem 1114 can modify the level of RF power generated by the RFpulse generator 1006. For example, for a moderate degree of reflectedpower the course of action can be for the controller subsystem 1114 toincrease the amplitude of RF power sent to the TX antenna 1010, as wouldbe needed to compensate for slightly non-optimum but acceptable TXantenna coupling to the body. For higher ratios of reflected power, thecourse of action can be to prevent operation of the RF pulse generator1006 and set a fault code to indicate that the TX antenna 1010 haslittle or no coupling with the body. This type of reflected-power faultcondition can also be generated by a poor or broken connection to the TXantenna. In either case, it may be desirable to stop RF transmissionwhen the reflected-power ratio is above a defined threshold, becauseinternally reflected power can lead to unwanted heating of internalcomponents, and this fault condition means the system cannot deliversufficient power to the implanted wireless neural stimulator and thuscannot deliver therapy to the user.

The controller 1142 of the device 1014 may transmit informationalsignals, such as a telemetry signal, through the antenna 1138 tocommunicate with the RF pulse generator module 1006 during its receivecycle. For example, the telemetry signal from the device 1014 may becoupled to the modulated signal on the dipole antenna(s) 1138, duringthe on and off state of the transistor circuit to enable or disable awaveform that produces the corresponding RF bursts necessary to transmitto the external (or remotely implanted) pulse generator module 1006. Theantenna(s) 1138 may be connected to electrodes 1154 in contact withtissue to provide a return path for the transmitted signal. An A/D (notshown) converter can be used to transfer stored data to a serializedpattern that can be transmitted on the pulse modulated signal from theinternal antenna(s) 1138 of the neural stimulator.

A telemetry signal from the implanted wireless device 1014 may includestimulus parameters such as the power or the amplitude of the currentthat is delivered to the tissue from the electrodes. The feedback signalcan be transmitted to the RF pulse generator module 1016 to indicate thestrength of the stimulus at the nerve bundle by means of coupling thesignal to the implanted RX antenna 1138, which radiates the telemetrysignal to the external (or remotely implanted) RF pulse generator module1006. The feedback signal can include either or both an analog anddigital telemetry pulse modulated carrier signal. Data such asstimulation pulse parameters and measured characteristics of stimulatorperformance can be stored in an internal memory device within theimplanted device 1014, and sent on the telemetry signal. The frequencyof the carrier signal may be in the range of at 300 MHz to 8 GHz.

In the feedback subsystem 1112, the telemetry signal can be downmodulated using demodulator 1122 and digitized by being processedthrough an analog to digital (A/D) converter 1120. The digital telemetrysignal may then be routed to a CPU 1130 with embedded code, with theoption to reprogram, to translate the signal into a correspondingcurrent measurement in the tissue based on the amplitude of the receivedsignal. The CPU 1130 of the controller subsystem 1114 can compare thereported stimulus parameters to those held in local memory 1128 toverify the stimulator(s) 1014 delivered the specified stimuli to tissue.For example, if the stimulator reports a lower current than wasspecified, the power level from the RF pulse generator module 1006 canbe increased so that the implanted neural stimulator 1014 will have moreavailable power for stimulation. The implanted neural stimulator 1014can generate telemetry data in real time, for example, at a rate of 8kbits per second. All feedback data received from the implanted leadmodule 1014 can be logged against time and sampled to be stored forretrieval to a remote monitoring system accessible by the health careprofessional for trending and statistical correlations.

The sequence of remotely programmable RF signals received by theinternal antenna(s) 1138 may be conditioned into waveforms that arecontrolled within the implantable device 1014 by the control subsystem1142 and routed to the appropriate electrodes 1154 that are placed inproximity to the tissue to be stimulated. For instance, the RF signaltransmitted from the RF pulse generator module 1006 may be received byRX antenna 1138 and processed by circuitry, such as waveformconditioning circuitry 1140, within the implanted wireless device 1014to be converted into electrical pulses applied to the electrodes 1154through electrode interface 1152. In some implementations, the implanteddevice 1014 contains between two to sixteen electrodes 1154.

The waveform conditioning circuitry 1140 may include a rectifier 1144,which rectifies the signal received by the RX antenna 1138. Therectified signal may be fed to the controller 1142 for receiving encodedinstructions from the RF pulse generator module 1006. The rectifiersignal may also be fed to a charge balance component 1146 that isconfigured to create one or more electrical pulses based such that theone or more electrical pulses result in a substantially zero net chargeat the one or more electrodes (that is, the pulses are charge balanced).The charge-balanced pulses are passed through the current limiter 1148to the electrode interface 1152, which applies the pulses to theelectrodes 1154 as appropriate.

The current limiter 1148 insures the current level of the pulses appliedto the electrodes 1154 is not above a threshold current level. In someimplementations, an amplitude (for example, current level, voltagelevel, or power level) of the received RF pulse directly determines theamplitude of the stimulus. In this case, it may be particularlybeneficial to include current limiter 1148 to prevent excessive currentor charge being delivered through the electrodes, although currentlimiter 1148 may be used in other implementations where this is not thecase. Generally, for a given electrode having several square millimeterssurface area, it is the charge per phase that should be limited forsafety (where the charge delivered by a stimulus phase is the integralof the current). But, in some cases, the limit can instead be placed onthe current, where the maximum current multiplied by the maximumpossible pulse duration is less than or equal to the maximum safecharge. More generally, the limiter 1148 may act as a charge limiterthat limits a characteristic (for example, current or duration) of theelectrical pulses so that the charge per phase remains below a thresholdlevel (typically, a safe-charge limit).

In the event the implanted wireless device 1014 receives a “strong”pulse of RF power sufficient to generate a stimulus that would exceedthe predetermined safe-charge limit, the current limiter 1148 canautomatically limit or “clip” the stimulus phase to maintain the totalcharge of the phase within the safety limit. The current limiter 1148may be a passive current limiting component that cuts the signal to theelectrodes 1154 once the safe current limit (the threshold currentlevel) is reached. Alternatively, or additionally, the current limiter1148 may communicate with the electrode interface 1152 to turn off allelectrodes 1154 to prevent tissue damaging current levels.

A clipping event may trigger a current limiter feedback control mode.The action of clipping may cause the controller to send a thresholdpower data signal to the pulse generator 1006. The feedback subsystem1112 detects the threshold power signal and demodulates the signal intodata that is communicated to the controller subsystem 1114. Thecontroller subsystem 1114 algorithms may act on this current-limitingcondition by specifically reducing the RF power generated by the RFpulse generator, or cutting the power completely. In this way, the pulsegenerator 1006 can reduce the RF power delivered to the body if theimplanted wireless neural stimulator 1014 reports it is receiving excessRF power.

The controller 1150 of the device 1105 may communicate with theelectrode interface 1152 to control various aspects of the electrodesetup and pulses applied to the electrodes 1154. The electrode interface1152 may act as a multiplex and control the polarity and switching ofeach of the electrodes 1154. For instance, in some implementations, thewireless stimulator 1006 has multiple electrodes 1154 in contact withtissue, and for a given stimulus the RF pulse generator module 1006 canarbitrarily assign one or more electrodes to 1) act as a stimulatingelectrode, 2) act as a return electrode, or 3) be inactive bycommunication of assignment sent wirelessly with the parameterinstructions, which the controller 1150 uses to set electrode interface1152 as appropriate. It may be physiologically advantageous to assign,for example, one or two electrodes as stimulating electrodes and toassign all remaining electrodes as return electrodes.

Also, in some implementations, for a given stimulus pulse, thecontroller 1150 may control the electrode interface 1152 to divide thecurrent arbitrarily (or according to instructions from pulse generatormodule 1006) among the designated stimulating electrodes. This controlover electrode assignment and current control can be advantageousbecause in practice the electrodes 1154 may be spatially distributedalong various neural structures, and through strategic selection of thestimulating electrode location and the proportion of current specifiedfor each location, the aggregate current distribution in tissue can bemodified to selectively activate specific neural targets. This strategyof current steering can improve the therapeutic effect for the patient.

In another implementation, the time course of stimuli may be arbitrarilymanipulated. A given stimulus waveform may be initiated at a timeT_start and terminated at a time T_final, and this time course may besynchronized across all stimulating and return electrodes; further, thefrequency of repetition of this stimulus cycle may be synchronous forall the electrodes. However, controller 1150, on its own or in responseto instructions from pulse generator 1006, can control electrodeinterface 1152 to designate one or more subsets of electrodes to deliverstimulus waveforms with non-synchronous start and stop times, and thefrequency of repetition of each stimulus cycle can be arbitrarily andindependently specified.

For example, a stimulator having eight electrodes may be configured tohave a subset of five electrodes, called set A, and a subset of threeelectrodes, called set B. Set A might be configured to use two of itselectrodes as stimulating electrodes, with the remainder being returnelectrodes. Set B might be configured to have just one stimulatingelectrode. The controller 1150 could then specify that set A deliver astimulus phase with 3 mA current for a duration of 200 us followed by a400 us charge-balancing phase. This stimulus cycle could be specified torepeat at a rate of 60 cycles per second. Then, for set B, thecontroller 1150 could specify a stimulus phase with 1 mA current forduration of 500 us followed by a 800 us charge-balancing phase. Therepetition rate for the set-B stimulus cycle can be set independently ofset A, say for example it could be specified at 25 cycles per second.Or, if the controller 1150 was configured to match the repetition ratefor set B to that of set A, for such a case the controller 1150 canspecify the relative start times of the stimulus cycles to be coincidentin time or to be arbitrarily offset from one another by some delayinterval.

In some implementations, the controller 1150 can arbitrarily shape thestimulus waveform amplitude, and may do so in response to instructionsfrom pulse generator 1006. The stimulus phase may be delivered by aconstant-current source or a constant-voltage source, and this type ofcontrol may generate characteristic waveforms that are static, e.g. aconstant-current source generates a characteristic rectangular pulse inwhich the current waveform has a very steep rise, a constant amplitudefor the duration of the stimulus, and then a very steep return tobaseline. Alternatively, or additionally, the controller 1150 canincrease or decrease the level of current at any time during thestimulus phase and/or during the charge-balancing phase. Thus, in someimplementations, the controller 1150 can deliver arbitrarily shapedstimulus waveforms such as a triangular pulse, sinusoidal pulse, orGaussian pulse for example. Similarly, the charge-balancing phase can bearbitrarily amplitude-shaped, and similarly a leading anodic pulse(prior to the stimulus phase) may also be amplitude-shaped.

As described above, the device 1014 may include a charge-balancingcomponent 1146. Generally, for constant current stimulation pulses,pulses should be charge balanced by having the amount of cathodiccurrent should equal the amount of anodic current, which is typicallycalled biphasic stimulation. Charge density is the amount of currenttimes the duration it is applied, and is typically expressed in theunits of uC/cm². In order to avoid the irreversible electrochemicalreactions such as pH change, electrode dissolution as well as tissuedestruction, no net charge should appear at the electrode-electrolyteinterface, and it is generally acceptable to have a charge density lessthan 30 uC/cm². Biphasic stimulating current pulses ensure that no netcharge appears at the electrode after each stimulation cycle and theelectrochemical processes are balanced to prevent net dc currents. Thedevice 1014 may be designed to ensure that the resulting stimuluswaveform has a net zero charge. Charge balanced stimuli are thought tohave minimal damaging effects on tissue by reducing or eliminatingelectrochemical reaction products created at the electrode-tissueinterface.

A stimulus pulse may have a negative-voltage or current, called thecathodic phase of the waveform. Stimulating electrodes may have bothcathodic and anodic phases at different times during the stimulus cycle.An electrode that delivers a negative current with sufficient amplitudeto stimulate adjacent neural tissue is called a “stimulating electrode.”During the stimulus phase the stimulating electrode acts as a currentsink. One or more additional electrodes act as a current source andthese electrodes are called “return electrodes.” Return electrodes areplaced elsewhere in the tissue at some distance from the stimulatingelectrodes. When a typical negative stimulus phase is delivered totissue at the stimulating electrode, the return electrode has a positivestimulus phase. During the subsequent charge-balancing phase, thepolarities of each electrode are reversed.

In some implementations, the charge balance component 1146 uses ablocking capacitor(s) placed electrically in series with the stimulatingelectrodes and body tissue, between the point of stimulus generationwithin the stimulator circuitry and the point of stimulus delivery totissue. In this manner, a resistor-capacitor (RC) network may be formed.In a multi-electrode stimulator, one charge-balance capacitor(s) may beused for each electrode or a centralized capacitor(s) may be used withinthe stimulator circuitry prior to the point of electrode selection. TheRC network can block direct current (DC), however it can also preventlow-frequency alternating current (AC) from passing to the tissue. Thefrequency below which the series RC network essentially blocks signalsis commonly referred to as the cutoff frequency, and in one embodimentthe design of the stimulator system may ensure the cutoff frequency isnot above the fundamental frequency of the stimulus waveform. In thisembodiment of the present invention, the wireless stimulator may have acharge-balance capacitor with a value chosen according to the measuredseries resistance of the electrodes and the tissue environment in whichthe stimulator is implanted. By selecting a specific capacitance valuethe cutoff frequency of the RC network in this embodiment is at or belowthe fundamental frequency of the stimulus pulse.

In other implementations, the cutoff frequency may be chosen to be at orabove the fundamental frequency of the stimulus, and in this scenariothe stimulus waveform created prior to the charge-balance capacitor,called the drive waveform, may be designed to be non-stationary, wherethe envelope of the drive waveform is varied during the duration of thedrive pulse. For example, in one embodiment, the initial amplitude ofthe drive waveform is set at an initial amplitude Vi, and the amplitudeis increased during the duration of the pulse until it reaches a finalvalue k*Vi. By changing the amplitude of the drive waveform over time,the shape of the stimulus waveform passed through the charge-balancecapacitor is also modified. The shape of the stimulus waveform may bemodified in this fashion to create a physiologically advantageousstimulus.

In some implementations, the wireless device 1014 may create adrive-waveform envelope that follows the envelope of the RF pulsereceived by the receiving dipole antenna(s) 1138. In this case, the RFpulse generator module 1006 can directly control the envelope of thedrive waveform within the wireless device 1014, and thus no energystorage may be required inside the stimulator itself. In thisimplementation, the stimulator circuitry may modify the envelope of thedrive waveform or may pass it directly to the charge-balance capacitorand/or electrode-selection stage.

In some implementations, the implanted device 1014 may deliver asingle-phase drive waveform to the charge balance capacitor or it maydeliver multiphase drive waveforms. In the case of a single-phase drivewaveform, for example, a negative-going rectangular pulse, this pulsecomprises the physiological stimulus phase, and the charge-balancecapacitor is polarized (charged) during this phase. After the drivepulse is completed, the charge balancing function is performed solely bythe passive discharge of the charge-balance capacitor, where isdissipates its charge through the tissue in an opposite polarityrelative to the preceding stimulus. In one implementation, a resistorwithin the stimulator facilitates the discharge of the charge-balancecapacitor. In some implementations, using a passive discharge phase, thecapacitor may allow virtually complete discharge prior to the onset ofthe subsequent stimulus pulse.

In the case of multiphase drive waveforms the wireless stimulator mayperform internal switching to pass negative-going or positive-goingpulses (phases) to the charge-balance capacitor. These pulses may bedelivered in any sequence and with varying amplitudes and waveformshapes to achieve a desired physiological effect. For example, thestimulus phase may be followed by an actively driven charge-balancingphase, and/or the stimulus phase may be preceded by an opposite phase.Preceding the stimulus with an opposite-polarity phase, for example, canhave the advantage of reducing the amplitude of the stimulus phaserequired to excite tissue.

In some implementations, the amplitude and timing of stimulus andcharge-balancing phases is controlled by the amplitude and timing of RFpulses from the RF pulse generator module 1006, and in others thiscontrol may be administered internally by circuitry onboard the wirelessdevice 1014, such as controller 1150. In the case of onboard control,the amplitude and timing may be specified or modified by data commandsdelivered from the pulse generator module 1006.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. Accordingly, otherimplementations are within the scope of the following claims.

What is claimed is:
 1. An implantation system, comprising: a styletcomprising an elongate member and a first mating feature at a distal endof the elongate member; and an implantable device configured to receivea wireless signal and to generate one or more electrical pulses from thewireless signal for exciting a tissue, the implantable devicecomprising: a cylindrical body defining a longitudinal axis of theimplantable device, a plurality of electrodes distributed along thecylindrical body and configured to deliver the one or more electricalpulses, an anchoring feature adjacent the cylindrical body and disposedproximal to the plurality of electrodes for securing the implantabledevice to the tissue, and a second mating feature disposed proximal tothe anchoring feature, disposed in-line with the longitudinal axis ofthe implantable device, and defining a proximal end of the implantabledevice, the second mating feature configured to mate with the firstmating feature such that the stylet and the implantable device can bedelivered percutaneously to a body of a subject together as an assembly;wherein the assembly of the stylet and the implantable device is sizedand shaped to be passed through a lumen of an introducer needle that isof gauge 18 or smaller and further through a percutaneous incision siteon the body, and wherein the stylet is sufficiently rigid such that theassembly of the stylet and the implantable device can be passed throughthe lumen of the introducer needle and further through the percutaneousincision site on the body.
 2. The implantation system of claim 1,wherein the stylet is a placement stylet.
 3. The implantation system ofclaim 2, wherein the first mating feature of the stylet includes aprotrusion and the second mating feature of the implantable deviceincludes an indentation, the protrusion being configured to mate withthe indentation.
 4. The implantation system of claim 1, wherein thestylet is a suction stylet that comprises a shaft, an inner plungerwithin the shaft, a suction tip, and an air chamber between the suctiontip and a distal end of the inner plunger.
 5. The implantation system ofclaim 4, wherein the stylet is configured to mate with the implantabledevice when a sliding motion of the inner plunger in the shaft creates anegative pressure in the air chamber to draw the second mating featureof the implantable device onto the suction tip.
 6. The implantationsystem of claim 1, wherein the anchoring feature comprises a passagewaythrough which a suture can be passed to secure the implantable device tothe tissue.
 7. The implantation system of claim 1, wherein theimplantable device further comprises an antenna for receiving thewireless signal.
 8. The implantation system of claim 1, wherein one ofthe first and second mating features has a convex profile and one of thefirst and second mating features has a concave profile.
 9. Theimplantation system of claim 1, wherein the plurality of electrodes iscylindrical in shape and is arranged in-line with the cylindrical body.10. The implantation system of claim 1, wherein the anchoring feature ispositioned along the longitudinal axis of the implantable device. 11.The implantation system of claim 1, wherein the implantable devicefurther comprises a smooth, round tip that defines a distal end of theimplantable device.